Re: MMC or Maxwell? Which is better?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Crow Leader" <tesla-at-lists.symmetric-dot-net> 

Here is my main point.

If you are not pushing the limits of the materials used, you don't need to
rely on self healing. The capacitor degrades as it "heals". My vacuum pump
doesn't have a self unbending shaft, it's thick enough where it will never
bend in the first place. I don't use asbestos fire resistant power cords, I
size them to never catch on fire in the first place.

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, February 26, 2004 9:00 PM
Subject: Re: MMC or Maxwell? Which is better?


 > Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
 >
 > Hi Ken,
 >
 >
 > >If I set out to collect flowers, I'd have a large collection as well. I'd
 > >bet a large number of the 50 aren't true RF duty rated caps, and would
have
 > >failed because of improper use. I can take the best 12 vold light bulb,
and
 > >it's going to fail if I plug it in an outlet.
 > >
 > >KEN
 >
 > One other thing about MMCs ;-))  They were designed from the ground up for
 > "Tesla coils".  So all the fudge factors and over design was directed
 > toward the common mistakes and mishaps "coilers" make.

Wrong. I don't see "designed for tesla coil use" in the cornell dublier
catalog anywhere.

 > The huge over voltage and self healing features are the biggest advantage
 > to help MMCs survive those resonant rise events that have killed so many
 > nice commercial caps (Terry filters save the NSTs ;-))
 >
 > The next big advantage are the simple charts for all kinds of NST coils so
 > folks can get exactly what they need (minimal cost) without having to
worry
 > about RMS current, voltage rating, and all kinds of nasty details that
also
 > kill commercial caps.  All the hard work is done.  One just follows the

These factors will kill any cap. Unless cornell dublier is some backwoods
garage operation, their prodcuts are "commercial" as well. Worrying about
currents seems valid in electrical projects. Why not ignore voltages too,
and grounding and all that stuff.

 > charts and gets the caps and they will work...  When I get Tesla coil caps
 > nowadays, shipping costs and delivery times are the only worry...  I
"know"
 > they will work perfectly fine once I get them...
 >
 > Of course, a commercial cap that is run on a Tesla coil within it's
 > voltage, current, etc. ratings will be fine aside from that defective cap
 > thing years ago...  But aside from the aluminum and plastic, there is also
 > a lot of testing and "work" that has gone into making MMCs "work" for
 > coilers.  In fact, I have never really thought about using them for
 > anything else!  Commercial caps make "you" do all the work, where with
 > MMCs, all the work is already done.

If figuring out what specs you need is too much work, one needs to drop any
sort of electrical hobby anyways. Even bowling as a sport requires some
math.

 > Another thing "I" always stress is that MMC have (should have) drain
 > resistors which I think vasty increases safety...  No worries about
 > residual charges on an MMC...

I recall they catch on fire alot, burning people's circuit boards. It shifts
the problems elsewhere.

 > Oh yeah!!  MMCs are also sold pretty much at cost.  There are no big
 > markups.  I think I lost a couple bucks on the 4000 I sold and I don't
 > think Chris is using his profits to pay off the Geek Lamborghini :o))
 >
 > I know there will always be people that want to use the commercial caps
and
 > that is fine.  They may be better on really high powered coils.  But I
 > don't think there is a lot of reason for the average coil builder to use
 > anything else unless they can't afford them.  In that case, the Geek
Bucket
 > cap...  But I think there is no doubt that the MMC directly caused the
 > instant extinction of the oil filled poly rolled cap ;-))  Remember them
:o)))
 >
 > An interesting thought, if one put a commercial 25kV 13nF commercial cap
in
 > parallel with a 25kV 13nF MMC*.  How would one blow up the MMC without
 > hurting the commercial cap??  Of course, blowing the commercial cap
without
 > hurting the MMC is easy ;-))

That should be pretty straight forward. For starters, make sure you are
using the self healing abilities with overstressed dielectric. As the
capacitance of the MMC cap assembly drops while the metallization burns
away, it will be stressed more and as the voltage across it increases.
Sounds like a spiral of destruction.

 > *Of course, one answer may be to directly short the thing at 20kV.  But
the
 > inherent inductance and ESR of the MMC will serve to protect
 > it.  Commercial caps are good to about 5 full dead shorts...  But the

Can you cite this only survives 5 crowbars rule of thumb?

Again, cornell dublier only makes residential and recreational capacitors.
This nonsense "commercial pulse cap" term needs to go away, it has no
meaning on this list. Like on ebay, people assume anything that says "tesla"
or "high voltage" is somehow "commercial" and "a pulse cap", or that
anything from Maxwell is rated the same. I'm pretty certain they make more
than one capacitor, and they all have different ratings. Try substituting "I
want to buy a Maxwell" with something as silly as "I want to buy a
Nichicon".

 > current in those shorts IS "cool"!!!  If you need those stunning currents,
 > you need commercial caps...  Coilers don't...

Hmm, use electrolytic caps then, they are pretty "slow" and have low pretty
low short circuit currents. Should be great for tesla coil.

KEN